From its very beginning, the Christian faith has been engaged with religious violence. The first Christians were persecuted by their co-religionists and then by imperial Rome. Jesus taught them, in such circumstances, not to retaliate, but to be peacemakers, to love their enemies, and to pray for their persecutors. Jesus's response to religious violence of the first century was often ignored, but it was never forgotten. Even during those centuries when the church herself persecuted Christian heretics, Jews, and Muslims, some Christians still struggled to bear witness to the peace mandate of...